In U.S. Pat. No. 3,879,293 a membrane diffusion device is disclosed having an inflatable member for pressurization and sealing. The inflatable member is U-shaped, to be positioned about the major faces and the bottom side of a stack of membrane sections separated by membrane support member means, and defining interleaving flow paths for two different fluids, separated by the membranes.
The purpose of an inflatable member, whether a flat member as is well known in the prior art, or the U-shaped member of the above patent, is to selectively apply pressure to the membrane stack by inflation while the stack is retained in a rigid casing, to prevent undue spreading of the fluid paths in the stack when pressurized fluid is provided. This is particularly important in the case where the device is intended for use as a blood oxygenator, an artificial kidney, or the like.
The invention of this application provides means for increasing the relative amount of surface area of the stack which is subjected to the effect of the inflatable shim. Also, a novel improvement in the end seal for the stack is provided, to further reduce the possibility of leakage from the ends of the membrane stack.